From the Department of Dermatology, Wellman Laboratory, Harvard Medical School, Massachusetts General Hospital, Boston. Dr Hruza is now at Washington University School of Medicine, St Louis, Mo; Dr Dover, New England Deaconess Hospital, Boston, Mass; and Dr Watanabe, Teikyo University School of Medicine, Tokyo, Japan.

• The Q-switched ruby laser is used for treatment of tattoos. The effects of Q-switched ruby laser pulses on sunexposed and sun-protected human skin, as well as senile entigines, were investigated with clinical observation, light microscopy, and transmission electron microscopy.

A pinpricklike sensation occurred at radiant exposures as low as 0.2 J/cm2. Immediate erythema, delayed edema, and immediate whitening occurred with increasing radiant exposure. The threshold for immediate whitening varied inversely with skin pigmentation, ranging from a mean of 1.4 J/cm2 in lentigines to 3.1 J/cm2 in sun-protected skin. Transmission electron microscopy showed immediate alteration of mature melanosomes and nuclei within keratinocytes and melanocytes, but stage I and II melanosomes were unaffected. Histologically, immediate injury was confined to the epidermis. There was minimal inflammatory response 1 day after exposure. After 1 week, subthreshold exposures induced hyperpigmentation, with epidermal hyperplasia and increased melanin staining noted histologically. At higher radiant exposures, hypopigmentation occurred with desquamation of a pigmented scale/crust. All sites returned to normal skin color and texture without scarring within 3 to 6 months.

These observations suggest that the human skin response to selective photothermolysis of pigmented cells is similar to that reported in animal models, including low radiant exposure stimulation of melanogenesis and high radiant exposure lethal injury to pigmented epidermal cells.